1. Field of the Invention
The present invention relates to a wave generator for ultra-high frequencies, more particularly a millimetric and sub-millimetric wave generator of the cyclotronic resonance maser type.
2. Description of the Prior Art
As generators of this type the generators called gyrotrons are known in particular. In these generators, an electron beam coming from an electron gun propagates along helicoidal paths while being guided by a uniform magnetic field directed along the axis of the helix. The beam passes then through an electromagnetic cavity resonating at a frequency f.sub.o close to a multiple of the cyclotronic frequency, in which cavity the transverse velocity components of the electrons interact with a transverse electric field component of the wave so as to give up their energy thereto. In this case, the beam is propagated substantially parallel to the magnetic field. Since the interaction takes place with the transverse velocity component v.perp. of the electrons, the parallel velocity component v.parallel. corresponds then to energy unused in the interaction. Efforts are therefore in general made to limit the value of this parallel velocity. However in the generators of the above type, it is not possible to operate with low values of v.parallel., for in this case an unstable electron beam is obtained. Consequently, the values of v.perp./v.parallel. must be chosen so that EQU 0.5&lt;v.perp./v.parallel.&lt;2